Lesson-1:Principles of Eco-Design(Part Five)

5,Embodied energy:

                               Embodied energy is the energy consumed by all of the processes associated with the production of a building, from the mining and processing of natural resources to manufacturing, transport and product delivery. Embodied energy does not include the operation and disposal of the building material. This would be considered in a life cycle approach. Embodied energy is the ‘upstream’ or ‘front-end’ component of the lifecycle impact of a home.

Every building is a complex combination of many processed materials, each of which contributes to the building’s total embodied energy. Renovation and maintenance also add to the embodied energy over a building’s life.

Choices of materials and construction methods can significantly change the amount of energy embodied in the structure of a building. Embodied energy content varies enormously between products and materials. Assessment of the embodied energy of a material, component or whole building is often a complex task.

If we want to reduce the total environmental impact of a building, we must consider the impact of the materials that have gone into its construction. Clearly no house can claim to be an eco-house if it is constructed from materials that had a major environmental impact elsewhere.

For these reasons, the concept of embodied energy is central to good environmental design. The embodied energy of a building material is the energy that has been required to extract, process, and manufacture it and then to transport it to the building site. The embodied energy in the structure of a new house is considerable, exceeding the total energy required to heat that house for the next 20 years.

In terms of the energy of manufacture, the highest embodied energy is found in metals (steel requires 57,000kWh to produce one cubic metre), and highly processed industrial products (hardboard and MDF require 2,000 kWh to produce 1m3). The middle range of materials are simpler to make but require a lot energy in their manufacture (bricks and concrete blocks need 700kWh/m3). The lowest embodied energy is in materials that require only simple processing (building timber needs 180kWh/m3 ) or those made from salvaged materials or local natural materials, which require virtually no energy.

The issue of embodied energy divides new eco-buildings into two distinct families. One kind of eco-building aims to obtain the lowest possible energy consumption with the most efficient available technology, such as high performance insulation and solar panels. Such buildings have a high embodied energy which they hope to justify with large savings in their energy consumption, or even to generate and export a surplus of energy. The other kind of eco-building aims to achieve the lowest possible embodied energy by using salvaged materials or simple local materials (straw bales, rush matting, mud bricks). Such buildings will usually perform less well in terms of annual energy consumption, and are less durable, but often have a lower overall environmental impact over the course of their lifespan.

Embodied energy is usually a good guide to wider environmental impacts, especially for toxic waste and atmospheric pollution. There are two main exceptions to this:

Cement and Concete, which has a mid range emobodied energy, but a disproportionately high impact on climate change. When limestone is burnt to make lime it releases an equal weight in carbon dioxide. Taken as a whole, the cement industry produces 5% of the worlds human carbon dioxide emissions.

Timber has a low embodied energy, but can have a very high environmental impact if taken from old growth forests.

Lesson -1: Principles of Eco-Design(Part Four)

4.Thermal zonning

                               -a thermal zone represents an enclosed space in wich the air is free to flow arround and whose thermal conditions are relatively consistent,in most cases any roomed closed with a door would be a separated zone but sometimes temperatures in different of large spaces can vary ,in wich cases the space can be divided into a number of small zones with adjoining elements defined as voids,in this way heat is free to flow among the zones but their thermal caracteristic can be analyzed individually.

                             -we like different temperatures in different rooms- we like bathrooms to be very warm, living rooms to be a comfortable cosy temperature, and bedrooms to be cooler, an efficient eco-design  recognises these differences and creates different thermal zones for the different rooms,some approximate figures for living temperatures are as follows:

Hot zone	20-23°	Bathrooms, airing cupboards, rooms for drying clothes, kitchen
Warm zone	18-21°	Living rooms, study, children's bedrooms
Cool zone	16-18°	Adult bedrooms
Cold zone	under 16°	Rooms that are not in use, storage rooms, garage, basement

                          -there are very great energy savings to be made from cutting just a couple of degrees off these temperatures, we live at the low end of these ranges and find that the maximum temperature we need is 19 degrees.

                          -thermal zoning tries to ensure the best match possible between the distribution of rooms and the distribution of the available heat, the ideal thermal zoning is:

• hot zone -the ideal place for hot rooms is in the very centre of the house, with no external walls so that the heat can radiate out into the rest of the house, the next best option is with a South facing window (which may be better for a bathroom where natural lighting and good ventilation is desireable.

• warm zone -the main living rooms need constant warmth and light and are best placed on the South side of the house with large windows and good thermal capacity to hold any thermal gain through the evening. Kitchens can generate a great deal of heat, the ideal location for a kitchen is therefore facing into the centre of the house, with the cooker placed on an internal wall.

• cool zone -adults tend to make little use of bedrooms except for sleeping and do not need to be especially warm, in a well insulated house a large part of their heating can be supplied by warmth rising from a well heated room below, adult bedrooms can be placed on the cooler side of the house,however, they need good light and an easterly window or skylight is preferred.

• cold zone -little used rooms are best located along the colder and darker North side of the house, rooms that need to be heated occasionally, such as a spare bedroom, perform better with a low thermal capacity with insulation on the inside of the room, storage rooms need to be kept dry but heat, light, and thermal capacity are of little concern, though the preference is for constant cool temperatures, basements and rooms under the stairs, if dry, are perfect for storage, durable items can be stored outside the insulated envelope altogether- such as under the eaves or in unheated sheds, in both cases the main concern is keeping them dry.

Lesson -1: Principles of Eco-Design(Part Three)

3.Stack effect:

-when air warms it expands, becomes less dense than the surrounding air, and rises,this process is called convection and is the main process by which heat moves around a room and the house, when rooms are sealed, convection is a sealed circuit of hot air rising over radiators and then sinking as it cools to be heated again.

-in reality, though, we don’t want rooms or houses to be fully sealed, ventilation with fresh air is vital in a healthy house, and convection plays a leading role in natural ventilation, hot air rises and escapes through small gaps in the building fabric at the top of the house, as it does so it draws in new cold air through similar gaps at the bottom of the house,the powerful suction created by escaping warm air is called the stack effect, or sometimes the chimney effect because it is the same process that draws smoke up a chimney or smokestack.
-stack effect is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers, and is driven by buoyancy,wich occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences, the result beeing either a positive or negative buoyancy force,as  the greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect.

-like many other environmental principles, the stack effect can either be a problem or an opportunity, it is the main motor generating draughts and the loss of hot air; and often the largest single cause of heat loss in a home,it requires particular attention when draughtproofing a house, however, when carefully controlled it can produce a low and effective level of natural ventilation and if respected and built into the house design, the stack effect is by far the most effective way of keeping a house ventilated in summer.

- over the past ten years environmental building has paid increasing attention to generating a stack effect to create natural ventilation, especially in large buildings, in a typical design tall chimneys at the top of the building create a powerful draw and fresh air is pulled into the building through specially placed controllable vents around the outside wall. 

-stack effect ventilation is an especially effective strategy in winter, when indoor/outdoor temperature difference is at a maximum, a chimney heated by solar energy can be used to drive the stack effect without increasing room temperature.

-in a modern high-rise building with a well-sealed envelope, the stack effect can create significant pressure differences that must be given design consideration and may need to be addressed with mechanical ventilation, also stairwells, shafts, elevators, and the like, tend to contribute to the stack effect, whereas interior partitions, floors, and fire separations can mitigate it, especially in case of fire, the stack effect needs to be controlled to prevent the spread of smoke.

Lesson -1: Principles of Eco-Design(Part Two)

2.Thermal mass:

• configure thermal mass to absorb sunlight-concrete, concrete masonry units (CMUs), brick, stone, and tile are typical materials used as thermal mass inside the building,the amount of glazing and insulation helps determine the amount of mass required to keep the house from overheating during the day and reduces the backup heat required during the night;

-thermal mass that is directly irradiated is much more effective than thermal mass that receives only reflected light,thermal mass requires that solar geometry be used as a design criterion for the placement of the mass;

-everything inside the house contributes to its thermal mass according to its capacity to absorb and store heat, known as its 'thermal capacity',the best materials for storing heat are those that are very dense, heat up slowly, and then give out that heat gradually: brick, concrete and stone have a high thermal capacity and are the main contributors to the thermal mass of a house, water has a very high thermal capacity, so it is well suited to central heating systems, air has a very low thermal capacity- it warms up fast but cannot stay warm for long, only when the walls and floors in a building have warmed up will the air stay warm.

• determine apropiate overhangs for all south glass
• limit east, west, and north glass while providing for cross-ventilation

-east and west windows lose as much heat as they gain, they are particularly problematic in regions with hot summers because they face the low solar angles in the mornings and afternoons,but they also provide an important function in creating cross-ventilation in rooms or for the entire house,also the  glazing becomes an important architectural feature, so the type of glass is important when placing east-west windows as the low solar heat gain glass can reduce the potential  overheating;

• design apropiate shading strategies for east and west glass

-the easiest way to limit summer heat gain through east and west windows is through strategic planting outside, trees and bushes that leaf out in summer and drop their leaves in fall provide for light and ventilation while shading the window when it is hottest outside,also you need to be  careful that the species selected doesn't grow too tall and lose its lower branches, thereby reducing its shading potential;

• calculate the backup cooling and heating required

-in a house insulated to current codes, thoughtful passive solar design can reduce the cost of heating and cooling by as much as 50%,in a superinsulated house, passive solar can replace even more fossil fuel than that, good design is the key, overheating is one of the main reasons that builders are skeptical of passive solar,there are some design softwares that can be  adjusted to take into account the passive solar contribution before sizing HVAC equipment. 

• insulate the house-insulating and air sealing the house are the perfect context for passive solar heating,when correctly installed with air sealing each type of insulation can deliver confort and lower bills during the hottest and coldest times of the year.

                    Eco-buildings are usually designed to have a high thermal mass for several reasons:

1. To hold over daytime solar gain for night time heating. A high thermal mass balances out the fluctuations in temperature that come from solar gain, soaking the extra daytime heat into the body of the building and releasing it slowly at night. The flywheel effect is most pronounced when the suns rays hit a wall or floor with high thermal capacity. For this reason eco-buildings are often designed with a dark coloured solid masonry wall and solid floor behind South facing windows.

2. To keep houses cool during the day in summer. A high thermal mass will reduce fluctuations in internal temperature during the summer. If a house has good ventilation during the night, its thermal mass can be cooled and it can then maintain that cool interior through the heat of the following day. In the extreme case of desert regions where daily temperatures can vary by up to 40°, traditional houses are usually designed to have extremely thick walls to moderate the internal temperature.

3. Increase the efficiency of a central heating boiler. A high thermal mass favours small boilers working at maximum efficiency, slowly and steadily raising the temperature of the building and then turning themselves off for sustained periods. Buildings with a low thermal mass, by comparison, tend to have much wider fluctations in temperature, and the boiler is constantly switching on and off to compensate.

To be continued...

Lesson -1: Principles of Eco-Design(Part One)

                From all the many theories behind environmental design, this section pulls out just a few core ideas. They are all important, and they provide the tools for approaching most design challenges:

1. Using the sun   
2. Thermal mass
3. Stack effect
4. Thermal zoning
5. Embodied energy

1.Using the sun-

• orient the house within 30 degrees of due south-due south is the equivalent of 100% potential solar heat gain through windows. Rotating the house to within 30 degrees of due south still provides about 90% of the potential solar gain and allows latitude for adjusting the house to lot limitations. Much further than 30 degrees starts to make architectural shading difficult and can lead to overheating;

          -only surfaces facing South receive sun all year round, the dominant direction of the sun  is from the South, especially in winter,for this reason, solar panels and windows that will capture solar warming in winter, should face as close to South as possible, solar receipts start to fall noticeably outside the band South-South-East to South-South-West, surfaces facing South-East or South-West receive 10% less solar energy during the year than surfaces facing due South;

- surfaces facing North are in the shade all year round,while most sun is received in the arc South East to South West, the adjacent quadrant, North-East to North-West, receives very little sun except at the peak of summer,for this reason solar design concentrates insulation and minimises glazing on this side of a house, new build solar houses often bury this side of the house in the ground and put all glazing on the South side of the house;

-the winter sun is low, the summer sun is high,vertical South facing windows work best for maximising solar heating in the winter as they capture the low winter sun,some solar  houses even have their windows angled 11 degrees back from the vertical to perfectly face the winter sun.

- surfaces that are more horizontal receive most of their sun in the summer, this is a problem for glazed roofs and skylights which receive little sun in winter but may well overheat rooms in summer,they usually need special shading or air vents (more on the design of roofs for porches and conservatories),the angle which receives the most sun across the year is, not surprisingly, 45°,for this reason it makes excellent sense to mount solar panels flush with a pitched roof;

-the high summer sun is a blessing when if comes to designing shading for vertical windows, only a small overhang is being needed to completely shade a vertical South facing windows in summer, this is another strong argument for maximising South facing glazing, East and West facing windows can be a huge nuisance in summer, they receive no direct sun in winter, but they fully face the low evening and morning sun in summer, West facing rooms are particularly prone to overheating and will need curtains or shades;

• use design software to optimize passive solar heating-this is a very important part if we want to make the house to work like a system, that we will discuss in a future lesson because this part  needs a lot more details like: softwares available,tutorials on how to use them and interpret the results and also integrate the results in our design/drawing scheme;